[T3] Temp sensor and MPS problems on new motor

[Keith Park]

Oh boy, Im all aglow!  FI RULES!  :-)


First off, where  is your AFR sensor?  it should be at the right end of a
stock muffler sensor angled down so it wont collect moisture.

only AFR readings at running speed mean anything, dont pay attention to idle
numbers.

What year is your car?

28 in the winter is WAY TOO LEAN, you could burn thru a piston that way.
you want mid 20's on the highway at 70, max.  That being said, your Stock FI
here in NY WILL NOT RUN PROPERLY on today's gas without richening it up.
You can make some difference by unplugging TS2, which is essentially what
you did, or raising the fuel pressure a few PSI but to do it correctly you
need to adjust the MPS.  This isnt a huge deal with the late ones but the
ones with a diaphragm in them you WILL screw them up unless you get in there
first and glue the bottom stop so when you turn the screw your not moving
that, you probably dont need to change the outer cover screw (plug).  This
is really getting DEEP into FI tuning, make sure you know what your doing
and prep up the CORRECT MPS for adjustment before you attempt changes, the
AFR Meter you have is essential here, you want 13-14 if I recall properly,
under light throttle on the highway, 10 with it floored.

Before Jim Adney chimes in... MAKE SURE your system voltage is up to 14+
volts running before making these changes, or your wasting your time as this
FI is VERY sensitive to system voltage but its too rich that they run when
the regulators get tired and voltage drops.  Start with a new solid state
regulator to eliminate those oddball readings, its $40 and well worth it
if your going to go thru the tuning procedure.

Dont even THINK about messing with the idle till you have the main mixture
right, as idle will likely be fine when the main mixture is right and its
not very easy to adjust the idle only mixture anyway.  Warmup curve is
adjusted with the AFR and TS1, you can get it pretty darn good with one
compression stroke starts but again, get the main mixture right first.

Sounds like your doing your homework, but Im sure Jim will chime in and add,
you can EASILY screw things up with the MPS if your not careful, I think he
has a way to adjust the C type back to stock again but as I said before,
stock wont run properly with today's NY gas, summer OR winter (although
the winter blend is a bit better)

Its important to get the mixture right, these motors dont last long if its
wrong but if correct... well, I tow all kinds of stuff with my Square and
that engine has over 150K on it now.

Keith

Topnotch Restorations
topnotch at nycap.rr.com
http://www.a383ina68.addr.com/radiorest/main.htm
71 Squareback  "Hothe"
65 Notchback  "El Baja Rojo"
93 RX7  "Redstur"
87 Golf  "Winterat"
 

-----Original Message-----
From: type3-vwtype3.org [mailto:type3-vwtype3.org-bounces at lists.vwtype3.org]
On Behalf Of Jessica Chase
Sent: Thursday, February 18, 2016 7:29 PM
To: type3-vwtype3.org at lists.vwtype3.org
Subject: [T3] Temp sensor and MPS problems on new motor

A month or so ago, my husband and I installed a new (stock) motor. After 2
smooth break in sessions and a few short drives, we took the car on a road
trip that we're still on! We installed our AFR gauge for the trip because we
wanted to monitor how things were running. 

Using the AFR gauge, in the fall, we were able to diagnose that we were
running lean with a new TS2 we installed. Adding 100O of resistance to the
sensor helped things out and everything was fine until yesterday. On the new
motor, we have the same TS2 and MPS (as well as all other FI components) as
on our previous motor, but now we're having trouble getting everything to
get along.  

At the outset of our trip, with the 100O resistor, the engine was lean
hunting at warm idle, so we tried a 200O ballast and resolved that issue.
However, AFR readings were slightly leaner than optimal, so we wanted to
perfect the system. 

I know not everybody on here (or maybe nobody on here) runs an AFR sensor
with the FI motor, but at warm idle, there should be an AFR of 13.1 and ours
was 14.2. There were no symptoms beyond getting slightly too good gas
mileage of 28mpg. But that's on winter gas in NYS and we barely get that in
the summer on highway trips so that's cause for suspicion.

Today, we decided to investigate. 

First, we got the timing and idle speed in spec.  The idle had been too high
and the timing too advanced. Once we dialed it in, the MPS we drove over 300
miles on yesterday would no longer idle.  It would lean hunt at high AFR and
then stall. What could that be about?

Second, we tried a different MPS - even though we ditched that one over the
summer because it had a vacuum leak and gave us strange readings.  Jim
checked it out and installed a new o-ring, but it still gives strange
readings.everything from 12.8 (rich) one moment to 18 or 20 (way lean..with
hesitation and bucking) with no change in speed or load.  
Third, we tried a NOS unit, but it, too, wouldn't hold idle for more than a
short while without stalling.  

Since TS2 required the 100O ballast over the summer to be happy, we tried
all three MPS's with both 100O and 200O ballasts.  We also tried all three
of them with nothing inline.  With the 100O ballasts and with nothing
inline, they all lean hunted and stalled.  With 200O ballasts, two of them
lean hunted and stalled.  The third (the one we ditched over the summer for
being inconsistent and wonky) idled richly and then continued to give
strange readings.  The only way we could continue to drive was to use this
third MPS with the 200O resistor even though it produces strange results. 

We removed TS2, let it cool off, and checked resistance readings of it and
another one we have.  Readings suggest it's fine: they are within 150 ohms
of each other at "room temperature." We also checked fuel pressure, and it's
fine too. 

It looks like we'll have to adjust the MPS, but does the situation we're
having sound familiar to anyone and did they find a solution? Our issues
with FI just seem to get weirder and weirder...!!!

Anyway, we have to drive 300 miles tomorrow and we don't want to have to get
towed so we're not too lean all the way back to NYC!!!



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